The present invention relates to improvements in lift truck-mounted clamping apparatus specifically for picking up, transporting and stacking large rolls of paper such as newsprint and kraft paper. More particularly the invention relates to improvements in the restraints utilized to limit the hinged motion of the roll-engaging contact pads mounted on the protruding ends of the clamp arms, and to means for preventing wear and resultant weakening of the hinge and tips of the contact pads.
Conventional lift truck-mounted paper roll clamps comprise a pair of forwardly-extending, selectively openable and closeable clamp arms mounted on a frame which in turn is rotatably carried by the lifting apparatus at the front of the lift truck, the frame being rotatable about a forwardly-extending axis. The rotation permits the clamp arms to engage the sides of cylindrical paper rolls regardless of whether the rolls are in vertical or horizontal positions, and to rotate the rolls from one position to the other. A small percentage of conventional paper roll clamps are not equipped with the rotation feature, and are thus limited to handling rolls in only one of the two alternative positions.
At each protruding end of the respective clamp arms a respective contact pad is normally mounted, such pad having an elongate, curved, concave roll-engaging surface extending transversely to the lift truck. Each contact pad is conventionally hingedly connected to its respective clamp arm so as to be pivotal with respect to the arm about an axis extending transversely of the lift truck. The hinged movement of the contact pads relative to the respective clamp arms serves several purposes, including permitting the pads conformably to engage the sides of cylindrical paper rolls of widely varying diameter, and permitting the pads to slide easily and comformably along the sides of the rolls without gouging their outer layers during initial engagement of the rolls by the clamp.
It has previously been determined that unrestrained hinged movement of the contact pads with respect to the clamp arms is undesirable because, without limitations on such movement, the pads can pivot far out of their proper positions making engagement of the paper rolls difficult. Accordingly it has been the practice to restrain the hinged movement of the contact pads with respect to the clamp arms to within predetermined limits by connecting a pair of rigid bars pivotally at one end to the rear longitudinal edge of each pad, the opposite ends of the bars being slidably connected to the respective clamp arm at interior positions within the arm structure. The slide structure conventionally includes stops fixed at appropriate locations within the clamp arm so as to limit the sliding movement of the bars, such stops determining the outer extreme of the hinged movement of the contact pad.
A number of problems have arisen from the use of the above-described conventional contact pad restraints in lift truck paper roll clamps. First, the durability of such restraints has generally been unsatisfactory at the slidable connection between the rigid bar and the clamp arm where shock-loading caused by the abrupt sliding engagement of the bar with a respective stop results in cracked welds and broken metal at these locations. Similar failures also occur at the pivotal connection between the opposite end of the bar and the contact pad. The problem is aggravated by the fact that the bars provide a very rigid connection with the contact pads which permits no cushioning of the shock.
Moreover, the size and strength requirements of the pad restraints in the past have dictated that they be located inwardly of the outer longitudinal edges of the clamp arms, the slide structures being located physically inside the arms. Such location has been a limiting factor with regard to the thinness of clamp arms near their protruding ends. It is desirable to provide as thin a structure as possible near the protruding end of a clamp arm so that the arm can easily be inserted between the sides of adjacent rolls or beneath a horizontally oriented roll. However the high strength requirements and resultant location and bulkiness of the conventional pad restraint slide structures, which are located near the protruding ends of the clamp arms, have limited the degree of structural thinness which can be obtained in the end region.
Moreover, the interior location of the slide structures within the body of the clamp arms has required that apertures be formed in the surfaces of the clamp arms to permit the bars to extend from the slide structures to the exterior of the clamp arms for connection to the pads. These apertures, which are of substantial size, weaken the clamp arm structure and cause stress concentrations where fatigue failures can occur. The apertures can also cause damage to adjacent rolls when the rolls are tightly stacked as in rail cars.
Another major problem which has existed in regard to paper roll clamp contact pads is the susceptibility to wear and resultant weakening of both the hinged joint between the pad and clamp arm and the tips of the pad at each longitudinal end thereof. The hinged joint is located on the rear side of the pad opposite its roll-engaging surface and extends longitudinally of the pad. Because the pad, in order to be inserted beneath a horizontally-lying roll, is often scraped along the floor during the insertion process, the rear surface of the pad and particularly the hinge can experience severe wear from frequent floor contact. The wear of the hinge, besides requiring costly replacement of pad or clamp arm components, can also constitute a danger to workmen if the gradual weakening of the hinge goes undetected and breakage occurs, causing the clamp to drop a paper roll.
A related problem exists with respect to the tips of the pad, located at each longitudinal end thereof, which also tend to become worm and weakened because of their contact with floors, walls, posts and other surfaces, particularly in view of the fact that the rotatability of the paper roll clamp permits a pad to be somewhat tilted with respect to the floor during insertion of the pad beneath a horizontal roll, thereby concentrating wear forces at one longitudinal end of the pad.